1. Field of the Invention
The present invention relates to a method and a copying machine for preventing illegal copying which are utilized to prevent illegal copying having been prohibited or being required to make impossible, for example, the illegal copying of banknotes, securities and the like, and particularly to a method and a copying machine for preventing illegal copying by which illegal copying is prevented with a less memory capacity by allowing only an illegal copying preventive pattern to be stored. The present invention also relates to an information carrying sheet of securities, identification cards and the like including an illegal copying preventive pattern which is readable by said copying machine or IR readers and hardly visible with the naked eye. The present invention further relates to an illegal copying preventive pattern comprising a plurality of patterns which have an absorption in different wavelength regions and are used in said sheet. The present invention still further relates to an IR absorption ink composition used for the illegal copying preventive pattern.
2. Background Art
Recently, as copying machines have been enhanced in performance, and particularly, high-performance color copying machines have been widely used, there have been frequent crimes of copying and counterfeiting securities such as banknotes, stock certificates, bonds, checks, bankbooks, lottery tickets, postage stamps and stamps, identification cards and the like such as passports and driver's licenses (hereinafter called banknotes and the like).
In order to prevent such crimes, as a crime prevention with respect to copying machine body, a copying machine has been developed which starts copying a subject to be copied only when previously stored image information of banknotes and the like is checked against the image information of the subject to be copied to reveal that both are not coincident with each other (as described in Nikkei Business issued on Apr. 27, 1992, page 29). The constitution of the copying machine is such that the copying machine is mounted with a ROM in which the image information of major banknotes throughout the world has previously been stored, and that if one attempts to copy a banknote having the same image information as that stored in the ROM, the two image informations to be checked against each other as previously described will be coincident, whereby the copying machine performs a predetermined crime preventive processing.
However, in the above-mentioned copying machine, major banknotes and the like of various countries in the world have to be stored in the memory thereof, thereby causing a problem of requiring an enormous memory capacity. Also, the copying machine, in performing copying operation, is required to retrieve a lot of image information in the memory to judge whether coincidence thereof exists or not, so that the copying machine have had a problem that waiting time has become very long because of the time required for the retrieval and for judging whether copying is acceptable or not.
On the other hand, as means for preventing the counterfeiting/altering with respect to the information carrying sheet becoming a subject to be copied, that is, to banknotes and the like, a method has been employed by which an illegal copying preventive image pattern readable mechanically by an IR reader is provided on a given area of the above-mentioned securities, identification cards and the like by the use of a printing ink containing an IR absorption material such as carbon black and IR absorption leuco dye. That is, the prevention of the former counterfeiting copy has been achieved by providing means capable of mechanically reading the above-mentioned image pattern on the copying machine body, and providing control means for stopping copying operation if the information pattern is read by the copying machine, while the truth or falsehood of the latter altered/falsified document has been judged by reading mechanically the prepared document with an IR reader to determine whether the above-mentioned image pattern exists or not.
However, the above-mentioned IR absorption material has an absorption even in visible region, and thus the existence thereof is liable to be read even by the naked eye, so that the IR absorption material has still been insufficient as means for preventing the above-mentioned crime. Although a heat ray absorption glass and a pigmented IR absorption glass which have recently been studied are applicable as an IR absorption material other than the above-mentioned material, a substantial amount of pigment is required to obtain a sufficient absorption, so that such material has had a disadvantage that such material becomes thicker in film thickness than conventional ink and thus the truth or falsehood of the document is naturally discriminated by the step difference.
Accordingly, in the above-mentioned various illegal copying preventive methods, a problem exists in that, for example, if common image information is recognized by an ill-intentioned third party, falsification is immediately performed to make invalid the information for the prevention of illegal copying. In order to prevent such illegal action, it is required that the application of such illegal copying preventive processing is not noticed by a third party whatever method is employed.
Therefore, an object of the present invention is to provide a method and a copying machine for preventing illegal copying which can promptly judge whether copying is acceptable or not with a less memory capacity to shorten copying processing time, and prevent securely an illegal action in such a manner that the application of an image pattern as an illegal copying preventive processing is not noticed easily by a third party.
Another object of the present invention is to provide an information carrying sheet of securities, identification cards and the like including an illegal copying preventive image pattern in which the existence of the above-mentioned image pattern is hardly discriminated by the naked eye.
Still another object of the present invention is to provide an illegal copying preventive image pattern which prevents an unnecessary exposure by combining a plurality of patterns having an absorption in different regions used in the sheet and incorporating a dummy pattern, and which is difficult to perform falsifying/altering/counterfeiting action.
Yet another object of the present invention is to provide an IR absorption ink composition which is used for the image pattern, hardly visible by the naked eye, and has a high IR absorption.